Catalytic indication methods for detecting the end point of the EDTA titration of Mn
2+and the precipitation titration of halide ions (Cl-, Br-, and I-) have been developed. As indicator reaction the coupling reaction of
p-phenylenediamine (I) and
m-aminophenol (II) catalyzed by traces of Mn
2+ in 0.4M hydrogencarbonate solution containing 0.06% hydrogen peroxide and that of (I) and
m-phenylenediamine (III) cataly zed by traces of Ag
+ are utilized. In contrast to oxidation products of single amine substrate, the absorption maximum of these coupling products shows a bathochromic shift and the solution turns instan taneously reddish violet (I-II) or violet (I-III) by the action of the metal ion catalyst. A mixed
o-toluylene diamine and (II) indicator system is also useful for catalytic titration of Mn
2+. This catalytic method has been applied to the substitution titration of Zn
2+, Cd
2+, and Pb
2+. In catalytic precipitation titration of halide ions, Br - and I- are titrated in aqueous solution, while Cl- is determined in non-aqueous or mixed solvent,
i.
e. methanol or 50% acetone. Milligram amounts of metal ions (Mn
2+, Zn
2+, Cd
2+, Pb
2+) and halide ions (Cl-, Br-, I-) are determined with the relative standard deviation of 0.1%,
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